The provided source excerpts are from E. A. Wallis Budge's translation of the "Book of the Dead," a collection of ancient Egyptian funerary texts. The excerpts describe the origins and development of the "Book of the Dead" from its earliest forms in the pyramid texts of the 5th and 6th dynasties to its use in later dynasties. The text also explains the ancient Egyptians' beliefs in the afterlife, including the importance of preserving the body, the journey of the soul to the underworld, and the resurrection of the deceased. The excerpts further outline the Egyptian pantheon of gods and their roles in the afterlife, as well as the rituals and ceremonies performed for the dead, particularly the "opening of the mouth" ceremony.